Talk about singular garnish (7)
I believe the answer is:
parsley
'garnish' is the definition.
(I have seen 'Herbal garnish ' mean 'parsley' so perhaps 'garnish' could also mean 'parsley')
'talk about singular' is the wordplay.
'talk' becomes 'parley' (to parley is to talk with an enemy).
'about' means one lot of letters goes inside another.
'singular' becomes 's' (abbreviation sometimes used in dictionaries).
'parley' enclosing 's' is 'PARSLEY'.
(Other definitions for parsley that I've seen before include "Aromatic herb with flat or crinkly leaves" , "Herbal garnish" , "Cow -, fool's - and stone - are all plants" , "Herb for garnishing" , "Food-flavouring herb for players" .)